hi PanchoSanza, I think that as long as your wrist is loose and it feels natural in movement to you during the serve is all that matters. i would not try to force the downward snap - the whole serve motion should be effortless. i tried things in the past to create more power and even though it helped in the beginning, in a long run i found myself with some chronic pains...
this following article can help you understand the serve technique even better: the art of the serve
have fun on the court!